The present invention relates generally to gas turbine engines, and, more specifically, to fans and compressors thereof.
A turbofan gas turbine engine includes a fan followed in turn by a multi-stage axial compressor each including a row of circumferentially spaced apart rotor blades, typically cooperating with stator vanes. The blades operate at rotational speeds which can result in subsonic through supersonic flow of the air, with corresponding shock therefrom. Shock introduces pressure losses and generates undesirable noise during operation.
In U.S. Pat. No. 5,167,489--Wadia et al, a forward swept rotor blade is disclosed for reducing aerodynamic losses during operation including those due to shock-boundary layer air interaction at blade tips.
However, fan and compressor airfoil design typically requires many compromises for aerodynamic, mechanical, and aero-mechanical reasons. An engine operates over various rotational speeds and the airfoils must be designed for maximizing pumping of the airflow therethrough while also maximizing compression efficiency. Rotational speed of the airfoils affects their design and the desirable flow pumping and compression efficiency thereof.
At high rotational speed, the flow Mach numbers relative to the airfoils are at their highest value, and the shock and boundary layer interaction is the most severe. Mechanical airfoil constraints are also severe at high rotor speed in which vibration and centrifugal stress have significant affect. And, aero-mechanical constraints, including flow flutter, must also be accommodated.
Accordingly, the prior art includes many fan and compressor blade configurations which vary in aerodynamic sweep, stacking distributions, twist, chord distributions, and design philosophies which attempt to improve rotor efficiency. Some designs have good rotor flow capacity or pumping at maximum speed with corresponding efficiency, and other designs effect improved part-speed efficiency at cruise operation, for example, with correspondingly lower flow pumping or capacity at maximum speed.
Accordingly, it is desired to provide an improved fan or compressor airfoil having both improved efficiency at part-speed, such as cruise operation, with high flow pumping or capacity at high speed, along with good operability margins for stall and flutter.